RU2688445C2 - System and method for determining information on basic physiological indicators of a subject - Google Patents

Abstract

FIELD: medicine.SUBSTANCE: group of inventions relates to remote photoplethysmography. Method for determining information on physiological indicators of a subject is carried out using a system for determining information on physiological indicators. Radiation received from the first and second marker regions, respectively, is detected. Information on physiological indicators of the subject from the detected radiation from the first and second marker regions is determined. System for determining information on physiological indicators of a subject comprises a carrier element carrying a marker for application on skin of a subject. Marker comprises first and second marker areas, each of which comprises an optical filter plate attached to the bearing member. First marker region is configured to transmit light at a first wavelength and to prevent light at a second wavelength, wherein modulation of light intensity is determined by time-varying reflection from skin at a first wavelength. Second marker region is configured to transmit light at a second wavelength and to prevent light at a first wavelength, wherein modulation of light intensity is determined by time-varying reflection from skin at a second wavelength. Reference area of the marker with a given reflection characteristic corresponding to the passing wavelength of the marker region is configured to calibrate the detection unit. Reference area is opaque and reflects light incident on it. Detection unit is configured to detect radiation received from first and second marker regions. Analysis unit is configured to determine information on physiological parameters of the subject from the detected radiation.EFFECT: unobtrusive determination of information on physiological indicators of the subject is achieved.11 cl, 7 dwg

Description

The present invention relates to a system and method for determining information about the main physiological parameters of a subject. In particular, the present invention relates to optical measurement methods that can be used to remotely determine the main physiological parameters of an examined subject. In this context, optical measurement may refer to photoplethysmography (PPG), more specifically to pulse oximetry.

BACKGROUND

Basic human physiological indicators, such as heart rate (HR), respiratory rate (RR), or blood oxygen saturation, are indicators of a person’s current state and effective indicators for predicting the onset of serious medical events. In this regard, the main physiological indicators are carefully monitored for hospital and outpatient treatment, at home or with additional health checks, on vacation and during fitness classes.

One of the ways to measure basic physiological parameters is plethysmography. Plethysmography, in general, concerns the measurement of changes in the volume of an organ or part of the body and, in particular, the detection of changes in volume caused by a cardiovascular pulse wave passing through the body of the subject with each heartbeat.

Photoplethysmography (PPG) is an optical measurement technology that evaluates a time-varying change in the reflection or transmission of light in the area or volume under investigation. PPG technology is based on the principle that the blood absorbs light more than the surrounding tissue, so that changes in blood volume with each heartbeat respectively affect the transmission and reflectivity. In addition to heart rate information, the PPG waveform may contain information related to an additional physiological phenomenon, such as respiration. By estimating the transmittance and / or the reflection coefficient for different wavelengths (usually the red and infrared regions of the spectrum), it is possible to determine the blood oxygen saturation.

Traditional pulse oximeters for measuring the heart rate and oxygenation of the subject are attached to the subject's skin, for example, the fingertip, the earlobe, or the forehead. Therefore, they are called “contact” PPG devices. A conventional pulse oximeter contains a red LED and an infrared LED as light sources, as well as one photodiode for detecting light transmitted through the patient's tissue. Commercially available pulse oximeters quickly switch between measurements at the red and infrared wavelengths, and therefore measure the transmittance of the same area or volume of tissue at two different wavelengths. This is called time division multiplexing. The transmittance in time dynamics at each wavelength allows to obtain PPG waveforms for the red and infrared wavelengths. Although contact PPG is considered to be essentially non-invasive technology, contact PPG measurement often causes discomfort because the pulse oximeter is directly attached to the subject, with any wires restricting freedom of movement.

Recently, non-contact remote PPG devices are presented for unobtrusive measurements. In a remote PPG, light sources are used or, in general, radiation sources located remotely from the subject being examined. Similarly, a detector, such as a camera or photo detector, may be located remotely from the subject being examined. Thus, remote photoplethysmographic systems and devices are considered imperceptible and suitable for everyday use in medical and non-medical purposes.

In a publication by Wieringa et al., "Contactless Multiple Wavelenghth Photoplethysmographic Imaging: A First Step Toward" Sp02 Camera "Technology," Ann. Biomed. Eng. 33, 1034-1041 (2005), disclosed a remote PPG system for contactless visualization of arterial oxygen saturation in tissue based on measurement of plethysmographic signals at different wavelengths. The system contains a monochrome CMOS-camera, as well as a light source with LED of three different wavelengths. The camera consistently receives three film fragments of the subject. During each film fragment the subject is illuminated by a light source at a different wavelength. The pulse rate can be determined from a film at one wavelength, while at least two films are required at different wavelengths to determine oxygen saturation. Measurements are taken in a dark room, using only one wavelength at a time. The patient is not allowed to move between successive measurements at different wavelengths. Another problem is that measurement in the dark is not constructive in areas of unobtrusive medical and non-medical use.

SUMMARY OF INVENTION

The present invention is to create an improved system and an improved method for an unobtrusive and economical determination of information about the main physiological indicators of the subject. It is preferable to create a system and method for working in natural light. In addition, it is preferable that the system and method allow parallel and possible real-time measurement of heart rate and oxygen saturation.

In the first aspect of the present invention, a system is presented for determining information about the main physiological parameters of a subject, comprising

- a marker for imposing on the skin of the subject, with the said marker additionally contains the first marker region, made with the possibility of transmitting light at the first wavelength, as well as the second marker area, made with the possibility of transmitting light at the second wavelength,

- a detection unit for detecting radiation received from the first marker region and from the second marker region of the marker, and

- analysis unit for determining information about the main physiological indicators of the subject from the detected radiation from the first marker region and from the second marker region.

In an additional aspect of the present invention, a marker is provided for use in the above system comprising a first marker region configured to transmit light at a first wavelength, a second marker region configured to transmit light at a second wavelength, while the marker is adapted to be applied to the skin the subject.

In an additional aspect of the present invention, an apparatus is presented for use in the above system comprising a detection unit for detecting radiation received from a first marker region, configured to transmit light at a first wavelength, as well as from a second marker region, configured to transmit light to a second wavelength, a marker imposed on the skin of the subject, as well as an analysis unit for determining information about the main physiological parameters of the subject from detected of radiation from the first marker region and from the second marker region.

In an additional aspect of the present invention, a method is proposed for determining information about the main physiological parameters of a subject, comprising:

- detection of radiation received from the first marker region, made with the possibility of transmitting light at the first wavelength, as well as from the second marker region, made with the possibility of transmitting light at the second wavelength, a marker superimposed on the skin of the subject, and

- determine the information about the main physiological indicators of the subject of the detected radiation from the first marker region and from the second marker region. In one embodiment, the method further comprises the step of applying the marker to the skin of the subject.

In another aspect of the present invention, a computer program is proposed comprising program code means for a computer to perform the steps of the proposed method when said computer program runs on a computer. In addition, a non-volatile medium is presented on which such a computer program is stored, which, being executed by a processor, leads to the implementation of the steps of the method disclosed in the present description. Preferred embodiments of the invention are defined in the dependent claims. It should be understood that the claimed marker, device, method, computer program and carrier have preferred embodiments of the same and / or identical preferred embodiments of the claimed system defined in the dependent claims.

The term "basic physiological parameters" in the context of the present invention refers to the physiological parameter of the subject and the derived parameters. In particular, the term “basic physiological parameters” contains heart rate (HR) (sometimes referred to as pulse rate), heart rate variability (pulse rate variability), pulse pressure, perfusion, perfusion index, perfusion variability, Traube-Hering waves- Mayer, respiratory rate (RR), body temperature, blood pressure, concentration of a certain substance in the blood and / or tissue, such as oxygen saturation or glucose content.

The term “basic physiological information” in the context of the present invention contains the measured one or more of the above basic physiological parameters. In addition, the term “basic physiological parameters information” contains data related to the physiological parameter, corresponding waveform records, or data related to the physiological parameter over time, which can be used for subsequent analysis.

The present invention is based on the idea that instead of consistently measuring in relation to the same area or volume of tissue at different wavelengths, information on basic physiological parameters can be obtained from spatially separated regions or volumes of tissue for which measurements are taken simultaneously. In other words, the inventors have found that it is possible to determine information about the main physiological parameters from a photoplethysmographic measurement at different wavelengths, performed on different spatially separated regions or volumes. This can be considered as space division multiplexing. The advantages lie in the fact that the measurement can be carried out under natural light conditions without the need for sequential narrow-band irradiation at different wavelengths, as proposed in the prior art.

According to one aspect of the present invention, a marker is provided comprising a first marker region configured to transmit light at a first wavelength, as well as a second marker region configured to transmit light at a second wavelength. The first marker region and the second marker region, thus, form spatially separate regions for determining information about the main physiological parameters. Each marker region is configured to transmit light at a different wavelength, so that the concentration of a substance can be determined based on a comparison of the light emission at two different wavelengths. The use of a marker has the advantage that no special additional filtering is required on the detection unit. A single detection unit can collect all the necessary information, thereby reducing the cost of the system.

As an option, the marker contains additional marker regions made with the possibility of transmitting light at additional wavelengths. The wavelengths of interest also include invisible electromagnetic wavelengths, including infrared and ultraviolet wavelengths.

In the context of the present description, the term "wavelength" also refers to a wavelength band or a range of wavelengths. It should be understood as a spectral range with a limited width of the spectrum. For example, with respect to an optical filter, the term “wavelength” refers to the passband of a filter. Consequently, the term “wavelength” is not limited to a single wavelength, but is also used for a range of wavelengths, for example, from several nanometers or several tens of nanometers, relative to the average wavelength. In addition, the term “wavelength” as applied to a filter can also refer to the set of discrete spectral ranges of the same filter element.

In the context of the present description, the term "detection unit" refers to a device for detecting electromagnetic radiation. It is designed to detect radiation received from the first marker region and from the second marker region. In a preferred embodiment, the detection unit is a camera having an image sensor, such as a CCD or CMOS image sensor, comprising a matrix of photosensitive pixels. The output of the detection unit refers to the radiation data. For example, radiation data is a series of images over time, i.e. video stream. The camera may be a monochrome or color camera. The RGB image sensor for a color camera contains a color channel filter matrix having filters for the red, green, and blue color channels. When using an RGB-color camera, the general filter characteristic of the system includes both the transmission characteristic of the marker regions and the filter characteristic of the camera color channels. In one embodiment, the transmission wavelength of the first marker region lies within the first of the RGB channels, and the transmission wavelength of the second marker region lies within the second RG channel. By appropriately selecting the transmission characteristics of the marker regions, the spatial separation of the first and second marker regions can be further supported by frequency-selective detection of the RGB camera. Thus, the requirements for the transmission characteristic of the first and second marker regions may become less stringent, while the cost of the system decreases.

Radiation received from the first or second marker regions usually contains two components. Firstly, the received radiation contains the light radiation reflected on the marker and / or on the skin surface, i.e. light radiation that does not penetrate the fabric and does not carry information about the absorption of light in the fabric. Secondly, the received radiation contains light that has penetrated the skin and is reflected from inside the tissue. This second part of the received radiation has a variable in time intensity due to a variable in time absorption and / or transmission of light in the tissue. The interaction of light with biological tissue is complex and involves the optical processes of (multiple) scattering, backscattering, absorption, transmission and (diffuse) reflection. The term “reflect” in this context means not only a specular reflection, but contains the above-mentioned types of interaction of light with a cloth, as well as all types of combinations thereof.

As an option, the system further comprises a light source for emitting light at said first wavelength and / or at said second wavelength to ensure that sufficient light is available at the appropriate wavelength. As an additional option, the system contains a control unit for adjusting the luminous intensity so that the detection unit can operate in its optimal operating mode, in particular so that, for example, noise or saturation effects do not interfere with the measurement. In a preferred embodiment, however, the system uses only natural light.

The analysis unit is configured to determine information about the main physiological parameters of the subject from the detected radiation from the first marker region and from the second marker region. The analysis unit receives radiation data from the detection unit. To determine the subject's heart rate, it is sufficient to estimate the time-varying radiation received from a single marker region or even from bare skin outside the marker region. However, to determine the concentration of a substance, for example, to determine blood oxygen saturation or glucose content, radiation analysis at different wavelengths is required, as described above. The analysis unit evaluates time-varying signals received from two spatially separated marker regions, and thereby evaluates two different wavelengths simultaneously. For example, the light emission received from the first marker region falls on the first pixel group of the image sensor constituting a part of the detection unit, and the light emission from the second marker region falls on the second pixel group of the image sensor. To increase the signal-to-noise ratio, the signals of the pixel groups can be combined.

According to a preferred embodiment, the system further comprises an image processing unit for recognizing the first marker region and the second marker region in the detected radiation. The image processing unit is an additional element located between the detection unit and the analysis unit. An image processing unit receives radiation data, such as a video stream, from a detection unit. The image processing unit comprises image processing means for recognizing a marker in received radiation data. For example, a marker has characteristic features that can be recognized in an image of a video stream. Analysis methods known from the field of image processing and video analysis can be used. In the marker, the first marker area and the second marker area are assigned to a specific place. Therefore, the image processing unit provides to the analysis unit processed radiation data containing information about the location of the first marker region and the second marker region in the radiation data. For example, an image processing unit identifies a pixel or a group of pixels representing portions of an image sensor that receive radiation from the first marker region, as well as pixels or a group of pixels that respectively receive radiation from the second marker region. The image processing unit may be embedded in the analysis unit.

In an additional embodiment, the system according to the present invention further comprises a carrier element bearing a marker. The carrier element specifies at least a first portion for placing the first marker region thereon, as well as a second portion for accommodating the second marker region thereon. In general, a carrier can be considered as an element that provides a mechanical support for a marker, for example, a plaster, a label or a similar structure that can be attached to the subject’s skin. The carrier may be made of a material belonging to a group of materials containing paper, cloth, rubber, or other materials used for adhesives, in particular medical patches.

In another embodiment, the carrier further comprises an adhesive for securing the carrier to the subject’s skin. Since, in a preferred embodiment, the carrier is directly attached to the skin of the subject, a biocompatible adhesive is used.

In yet another embodiment, the first marker region and / or the second marker region comprise an optical filter plate attached to the carrier element. The optical filter plate provides the transmission of light radiation only the desired wavelength or wavelength band. The types of filter plates include absorption filters as well as dielectric filters. Preferably, the carrier element comprises an aperture, wherein the optical filter plate is located in said aperture. The hole is also called a window or an optical window.

According to an alternative embodiment, the marker comprises a first dye applied to the subject’s skin in the first marker region and / or a second dye applied to the subject’s skin in the second marker region. Instead of using an optical filter plate in this embodiment, colored dyes are used, with the first dye transmitting light at the first wavelength, and the second dye transmitting light at the second wavelength. While the plates of optical filters are usually attached to the carrier, dyes can be applied directly to the subject's skin, without the need to use the carrier.

In an additional embodiment, the marker further comprises a reference region with a specified reflection characteristic. This reference area can be used to calibrate the detection unit, since the reflection characteristic for a given wavelength range is known. In particular, when the system is equipped with an optical light source and a control unit, the reference area in the detected radiation can be used to adjust the sensitivity of the detection unit and / or to adjust the power and / or spectrum of the light source. The marker can also contain more than one reference area, with each reference area having an excellent reflection characteristic. For example, the red reference region is used to determine the power of optical radiation in the red region of the spectrum, while the reference region in which infrared light is reflected is used to determine the optical radiation power in the infrared region of the spectrum. Based on these measurements, the sensitivity of the detection unit can be adjusted. Alternatively, time is adjusted to achieve a sufficiently high signal-to-noise ratio.

According to a further aspect of this embodiment, the reference area is opaque. In other words, the reference area blocks any light radiation passing through the marker, and only reflects the light falling on the reference area. This ensures that the radiation received from the reference area is essentially free from interference, in particular, does not contain reflected or back-scattered radiation from the underlying tissue. Thus, the light emission from the first and / or second marker region provides plethysmographic information, while the light emission from the reference region does not carry plethysmographic information and is for reference only.

In addition, the reference area can be used to determine any temporal or spectral interference from natural light or a source of artificial light, such as slow changes during the day or systemic effects, such as 50/60 Hz flicker or pulse width modulation of the light source. Corrections for such interference may be introduced into the measured radiation intensity from the first and / or second marker region.

In yet another embodiment, the marker further comprises a graphic pattern. The graphic pattern is designed to be detected in radiation data by an analysis unit or an additional image processing unit. Preferably, the graphic pattern has a high contrast image, such as a black and white pattern. Alternatively, the graphic pattern contains various colors that can be easily distinguished from each other. Preferably, the graphic pattern is in a machine-readable form, for example, in the form of a barcode, a matrix barcode, alphanumeric characters, a QR code, and the like. For an image processing unit, it is easier to recognize a specified graphic pattern in an observed image than to analyze vague features of an image. As an option, the graphic pattern is a machine-readable code that stores information, such as a patient identifier, for assigning the obtained information about the basic physiological parameters to the patient or a part of the patient’s body. Encoded information may contain configuration data to create a system configuration for determining information about basic physiological parameters, such as necessary sensitivity, or data relating to information about basic physiological indicators that need to be measured. The layout of the first marker region and the second marker region, as well as the size and / or shape of the supporting element can also be considered as a graphic pattern.

As an option, markers can be made or customized by applying different layers of ink or dyes to the carrier. The color and opacity of the ink can be adjusted so as to ensure the passage or blocking of the corresponding intensity and spectral components. Alternatively or additionally, the graphic pattern may be printed as part of the marker.

In a further embodiment, the first marker region and / or the second marker region contain subregions. In other words, the marker region may consist of a plurality of smaller sections. For example, the subregions of the first marker region and / or the second marker region are staggered. This ensures that the first marker regions and the second marker regions are not too far apart, while the common marker region still covers the desired skin area.

According to another aspect of the system of the present invention, the marker further comprises a stimulant for enhancing blood perfusion in the tissue of the subject in contact with the marker. As explained above, photoplethysmography is based on changes in the volume of blood vessels in the tissue. Therefore, to increase the signal power, it is desirable to ensure sufficient blood flow in the vessels under the marker, when the marker is applied to the subject, the main physiological parameters of which are required to be determined.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will become apparent from the embodiments described below. On the following drawings

in FIG. 1 shows an example implementation of a system for determining information about the main physiological parameters of a subject according to the present invention;

in FIG. 2 shows the definition of basic physiological information using the system according to the present invention;

in FIG. 3 shows a first marker example;

in FIG. 4 shows a second marker example;

in FIG. 5 shows a third marker example;

in FIG. 6 shows an example of a marker having sub-regions;

in FIG. 7 shows an alternative example of a marker having subregions.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an example implementation of system 1 for determining information 7 about the basic physiological parameters of subject 100 according to the present invention. The system 1 contains a marker 10 for applying to the skin of the subject 100, a detection unit 2, as well as an analysis unit 6 as main components. In this example, the system for determining information about the main physiological indicators of the subject is used in a hospital setting where subject 100 lies in bed 103.

The marker 10 further comprises a first marker region 11, configured to transmit light at a first wavelength, and also a second marker region 12, configured to transmit light at a second wavelength. The detection unit 2 is configured to detect radiation received from the first marker region 11, as well as from the second marker region 12 of the marker 10. In this example, the detection unit 2 is connected to the additional image processing unit 4. The detection unit 2 provides radiation data 3, representing the detected radiation, to the image processing unit 4 as a stream of video data. The image processing unit 4 identifies the first marker region 11 and the second marker region 12 in radiation data 3. The image processing unit 4, in turn, is connected to the analysis unit 6. The image processing unit 4 provides the pre-processed radiation data 5 to the analysis unit 6. The pre-processed radiation data 5 in this example contains information about which region of the images of the video data stream 3 about the radiation represents the first marker region 11 and the second marker region 12. Analysis unit 6, in turn, determines information 7 about the main physiological parameters of the subject from time-varying intensity in the first marker region 11 and in the second marker region 12. In this example, information about the main physiological indicators contains heart rate and saturation blood oxygen.

The image processing unit 4 for recognizing the first marker region 11 and the second marker region may also be included in the analysis block 6. Alternatively, radiation data 3 is directly provided to analysis block 6. In this case, both the first marker region 11 and the second marker region 12 can be determined by manually selecting the marker regions in the images of the video stream. Alternatively, subject 100 with marker 10 should be located in a predetermined position in the field of view of detection unit 2, so that the first marker region 11 and the second marker region 12 are in a predetermined position. However, the automatic identification of the marker 10 in the radiation data 3 by the image processing unit 4 is preferred.

In the example shown, the marker 10 is directly applied to the open skin of the forehead 101 of the subject 100. The alternative marker 10 'having the first marker area 11' and the second marker area 12 'is located on the left forearm 102 of the subject 100. The size and shape of the marker 10, 10' can chosen depending on the anatomical location.

The scene is illuminated by a radiation source, such as sunlight 7a or an artificial light source 7b. The radiation source 7a, 7b directly or indirectly emits radiation 8a, 8b in the direction of subject 100. In addition or alternatively, system 1 may also contain an additional system light source 7c emitting light 8c in the direction of subject 100. Using the system light source 7c is particularly useful if the ambient light sources 7a, 7b do not provide enough light or if the spectrum of the ambient light sources 7a, 7b does not have sufficient power at the first wavelength and at the second wavelength.

The additional control unit 9 is configured to adjust the sensitivity of the detection unit 2 and / or adjust the power of the system light source 7c. Since the dynamic range of the detector or image sensor used as detection unit 2 is limited, the gates and electronic compensations may need to be adjusted according to the lighting condition in the observed image. The light source 7c of the system may be part of the control loop setting the optimum operating mode of the image sensor of the detection unit 2. The term “optimal” in this context refers to the output signal without distortion, the lack of saturation of individual detectors or image sensors, as well as a high signal-to-noise ratio, at least for the area of the sensitive surface of the detector corresponding to the first and / or second marker areas.

FIG. 2 illustrates the determination of information about the main physiological parameters of a subject using system 1 according to the present invention. FIG. 2 shows a light source 21, a detection unit 22, as well as a marker having a first marker region 23 and a second marker region 24. The marker is applied to the dermal tissue 104 of the subject. The tissue contains blood vessels 105.

In this embodiment, the light source 21 emits light at least at a first wavelength (marked with dotted lines) and a second wavelength (marked with dashed lines). The first marker region 23 is adapted to transmitting light at a first wavelength, wherein said first wavelength corresponds to a first wavelength of the source 21 of the light. The second marker region 24 is adapted to transmitting light at a second wavelength, wherein said second wavelength corresponds to a second wavelength of the source 21 of the light. FIG. 2 schematically shows two light beams A, B at the first wavelength and two light beams C, D at the second wavelength. Since the first marker region 23 is configured to transmit light at the first wavelength, beam A passes through the marker and penetrates the skin 104 of the subject 100. Some of the light is absorbed by the skin 104, and some of the light is reflected or scattered into the tissue and reaches the detection unit 22. The characteristic of absorption and / or reflection changes over time and represents the time-varying perfusion of tissue 104 through its blood vessels 105.

The detection unit 22 comprises receiving optics, for example, receiver lenses, as well as a matrix of 25 photodetectors or pixels forming the image sensor. The light emission received from the first marker region is visualized on the first group or matrix of pixels 26. Accordingly, the light emission received from the second marker region 24 is visualized on the second group of pixels 27.

Since the absorption of light in the fabric 104 varies with time, the intensity of the light incident on the image sensor of the detection unit 22 also varies with time. The time-variable intensity in the region of pixels 26 is depicted by curve 28. The time-varying intensity of light falling on a group of pixels 27 is depicted by curve 29.

Since the first marker region is configured to transmit light only at the first wavelength, the light at the second wavelength does not pass through this marker region and does not penetrate the tissue, as indicated by the light beam C. However, part of the light emission can be scattered in the opposite direction on the surface of the marker and reach detection block 22. This light emission is not modulated by a pulsating change in blood volume and causes an error. The intensity modulation shown by curve 28 is thus caused by the time-varying reflection in tissue 104 at the first wavelength.

Accordingly, the light beam D at the second wavelength can pass through the second marker region 24, while the light beam B at the first wavelength is not transmitted. The intensity modulation shown by curve 29 is thus caused by the time-varying reflection in tissue 104 at the second wavelength.

The subject's pulse rate can be directly determined from the time-variable intensity from one of the curves 28 or 29. However, at least two wavelengths are required to determine blood oxygen saturation using photoplethysmography, as explained in the example below.

Contact pulse oximeters typically transmit red (R) or infrared (IR) light (or, more precisely, in some cases, near-infrared light) through the vascular tissue of the subject under study. The corresponding parts of the light emission (R / IR) can be skipped and detected alternately (in the fast switching mode). Given that the corresponding spectral regions are absorbed differently by oxygenated hemoglobin (Hb0 ₂ ) and restored hemoglobin (Hb), in the end, it is possible to calculate the blood oxygen saturation. The algorithm for estimating oxygen saturation (S0 ₂ ) can use the ratio of signals associated with the red and infrared part of the spectrum. In addition, the algorithm can take into account the non-pulsing component of the signal. Typically, a PPG signal contains a DC component and a relatively small pulsating AC component. In addition, an estimate of S0 ₂ typically involves the use of an empirically derived calibration factor applied to the calculated values. Usually, the calibration factor (or calibration curve) is determined after carrying out reference measurements, including invasive measurements of blood oxygen saturation. The calibration factor is necessary because the PPG device essentially determines the ratio between the parts of the (spectral) signal, which should be translated into the value of blood oxygen saturation, usually including the ratio between Hb0 ₂ and Hb. For example, but not for the purpose of limiting the present disclosure, an estimate of blood oxygen saturation may be based on the following general equation:

SO ₂ = Hb0 ₂ / (Hb0 ₂ + Hb), (1)

however, PPG devices only indirectly determine HbO ₂ and Hb from the spectral characteristics at least at two wavelengths.

In general, the measured intensity curve 28, 29 used as a characteristic signal is considered as containing a constant (DC) section and a variable (AC) section superimposed on the DC section. By applying signal processing techniques, the AC portion can be selected, and in addition, noise corrections can be introduced. For example, the AC portion of the characteristic signal may contain a dominant frequency, which may be very indicative of the vascular activity of the subject 100, in particular the heartbeat. At the same time, the characteristic signal, in particular the AC portion, may be indicative of other vital parameters. In this regard, the definition of arterial oxygen saturation is an important area of application. As indicated above, essentially the values representing the oxygen saturation of the blood can be calculated taking into account the nature of the change in the AC portion of the characteristic signal in its discrete spectral regions. In other words, the degree of saturation of arterial blood with oxygen can be reflected in the unequal absorption of radiation on blood vessels. In addition, the fact that the difference in absorption due to the degree of oxygen saturation can also vary considerably in different spectral regions can be used. In addition, the DC signal portion can also be used to determine blood oxygen saturation. Typically, the DC component represents the total absorption of light by tissue, venous blood, and non-pulsating arterial blood. On the contrary, the AC component may represent the absorption of pulsating arterial blood. Therefore, the definition of arterial oxygen saturation (Sa0 ₂ ) can be expressed as follows:

SaO ₂ = C (AC / DC) red / (AC / DC) infrared, (2) where C is the calibration factor. Coefficient C may denote a variety of calibration coefficients applicable to the AC / DC ratio, and therefore, should not be perceived in the strictly algebraic sense of equation (2). The coefficient C, for example, may represent a value having a constant value, a set of constants or an adjustable calibration factor. As an example, another typical model for obtaining Sa0 ₂ can be expressed as follows:

SaO ₂ = C ₁ + C ₂ (AC / DC) red / (AC / DC) infrared, (3) where C ₁ and C ₂ can be considered as linear approximation calibration coefficients. In one embodiment, the determination of the signal calibration factor may be directed to adjusting or adjusting the coefficient C ₁ . In addition, alternatively, obtaining Sa0 ₂ can also be based on tables of values entered into device 1 (or those available to it). Value tables (or databases) can provide a discrete representation of the relationship between the recognized PPG signals and the required calibration factor. In this case, a custom calibration factor can also be used to improve the accuracy of determining vital signs.

It should be understood that equations (2) and (3) are presented mainly for illustrative purposes. They should not be construed as limiting the scope of the present disclosure. In practice, the specialist will be able to propose additional relevant models for determining Sa0 ₂ . Alternative combinations of wavelengths, for example in the green and red regions of the spectrum, can be used depending on the substance to be recognized. Although the measurement of Sa0 _{2 has} been described in detail, it should be understood as an example of a general concept of measuring the concentration of a substance in the blood and / or tissue.

FIG. 3 shows in more detail an embodiment of a marker for use in system 1 for the purpose of determining information about the main physiological parameters of a subject according to the present invention. Marker 30 has a first graphic pattern 32, a second graphic pattern 33, reference regions 34a, 35a, 36a, 37A, marker regions 34b, 35b, 36b, configured to transmit light at three different wavelengths, as well as transparent marker region 37b.

The carrier element 31 is the carrier of the marker 30 with its elements, and also provides mechanical stability. In this embodiment, the carrier 31 is a plaster or adhesive plaster, which can be directly attached to the skin of the subject 100 using an adhesive. The bearing element is made of opaque rubber-like material that does not transmit light. In this regard, the carrier has holes or windows at the locations of the marker regions 34b, 35b, 36b, 37b.

An optical filter plate is arranged in each of the windows 34b, 35b, 36b, wherein the filter plate 34b is adapted to transmit light at a first wavelength, the filter plate 35b is adapted to transmit light at a second wavelength, and the filter plate 36b is adapted to pass light at the third wavelength. The marker area 37b does not have a frequency-selective filter and is transparent, so that the skin under area 37b is visually accessible to the detection unit as a reference area of the skin not covered by the filter.

Reference areas 34a, 35a, 36a are reference areas for specific wavelengths. Preferably, the color of the reference region corresponds to the transmission wavelength of the adjacent filter. For example, the marker region 34b is configured to transmit red light, while the reference region 34a is red so that it can serve as a pointer, in particular, how much red light is in the radiation incident on the marker.

Graphic pattern 32 serves as a display indicator. The geometric design allows the image processing unit 4 to determine the position and / or orientation of the marker 30. Marker 30, in addition, has a machine-readable graphic pattern 33 in the form of a QR code. This code contains information about the subject, so that the obtained information about the main physiological indicators can be attributed to the subject, for example, entered into an electronic medical record (EHR). The code may also contain information about the area in which the marker is attached to the body of the subject, so that at the same subject various measurements can be carried out individually for the measurement site (for example, the forehead and the arm).

Although FIG. 3 presents many features, not all of them are required. FIG. 4 shows the basic configuration in which there are two marker regions. In this example, the marker contains the first dye applied directly to the skin of the subject in the first marker region, as well as the second dye applied directly to the skin of the subject in the second marker region. The dye may be, for example, an elastomer, stamped, drawn, sprayed or printed on the skin. The dye of the first marker region is adapted to transmitting light at the first wavelength, while the dye in the second marker region is adapted to transmitting light at the second wavelength. Accordingly, an additional reference area may be applied.

FIG. 5 is a side view of a marker similar to that shown in FIG. 3. It is fixed on the skin of the 104 subject. The carrier 51 imparts mechanical stability to the marker 50. On the side of the carrier 51, facing the skin 104 of the subject, the carrier 51 contains an adhesive 52 for attaching the carrier to the skin 104 of the subject. The adhesive 52 further comprises a stimulator to increase the blood perfusion in the tissue of the subject 104, in contact with the carrier element 51, on which the marker 50 is located.

On the opposite side of the carrier 51, the marker 50 has reference areas 54a, 55a, as well as a first marker area 54b, adapted to transmit light at a first wavelength, and a second marker area 55b, configured to transmit light at a second wavelength. This is achieved due to optical filter plates 56, 57, located on the site of the first and second marker areas and laminated to the carrier 51. As an option, the adhesive is not applied in the marker areas 54b, 55b so as not to affect the transmission characteristic of the marker areas.

FIG. 6 and 7 show various patterns of optical windows along with the first and second marker regions, as well as reference regions. In this example, the first and second marker regions are divided into subregions. Reference area patterns and optical windows containing the first and second marker regions can be selected according to the needs in a particular dimension.

For some measurements, it is important to obtain signals for each wavelength from closely located areas of tissue. In this case, it is preferable to have several smaller optical windows, for example, staggered. FIG. 6 shows a staggered marker 60 for two wavelengths with alternating reference regions 61a and first marker regions 61b for the first wavelength, as well as reference regions 62a and second marker regions 62b for the second wavelength. For example, to measure blood oxygen saturation, the red region of the spectrum is used as the first wavelength, and the infrared region of the spectrum is used as the second wavelength.

FIG. 7 shows an alternative embodiment of the marker 70, while the distribution of the reference regions 71a, 72a and optical windows for the first and second marker regions 71b, 72b is optimized depending on the expected signal power. For example, the signal at the first desired wavelength, such as the green spectrum, is more powerful than the signal at the second desired wavelength, such as the red spectrum. Thus, the common second marker region 72b is increased relative to the common first marker region 71b in order to achieve the same signal power at both wavelengths.

As an example, the present invention can be applied in the field of health care, for example, for unobtrusive remote patient monitoring, general observation, security monitoring and in so-called lifestyle-defined environments, for example, in fitness equipment, etc. Applications may include monitoring oxygen saturation (pulse oximetry), heart rate, blood pressure, cardiac function, changes in blood perfusion, assessment of autonomic functions, and the detection of peripheral blood vessel disease.

Although the invention is illustrated in the drawings and is described in detail in the above description, these illustrations and the description should be considered as an example, but not limiting; The invention is not limited to the disclosed embodiments. Specialists in this field of technology will be able to offer and implement other modifications of the disclosed embodiments, applying in practice the claimed invention, having examined the drawings, the description and the attached claims.

In the claims, the term "comprising" does not exclude the presence of other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several items listed in the claims. The fact that certain measures are mentioned in the mutually distinct dependent claims does not mean that a combination of these measures cannot be used to advantage.

The computer program may be stored / distributed on a suitable non-volatile medium, such as optical media or solid-state media, supplied with or in part to other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless media. telecommunication systems.

None of the reference positions should be construed as limiting the scope of the invention.

Claims (22)

1. The system (1) for determining the information (7) about the physiological indicators of the subject (100), containing the carrier element (31, 51), carrying the marker (10, 10 ', 30, 40, 50, 60, 70) for overlay on the skin (104) of the subject, with the above-mentioned marker additionally contains: the first marker region (11, 11 ', 23, 34b, 41, 54b, 61b, 71b), moreover, the first marker region contains a plate of the optical filter attached to the carrier element, moreover, the first marker region is configured to transmit light (A, B) at the first wavelength and to transmit light at the second wavelength, and the modulation of the light intensity is determined by the time-varying reflection from the skin at the first wavelength, the second marker region (12, 12 ', 24, 35b, 42, 55b, 62b, 72b), moreover, the second marker region contains a plate of the optical filter attached to the carrier element, moreover, the second marker region is arranged to transmit light (C, D) at the second wavelength and to transmit light at the first wavelength, and the modulation of the light intensity is determined by the time-varying reflection from the skin at the second wavelength, moreover, the marker further comprises a reference area with a given reflection characteristic corresponding to the transmission wavelength of the marker area, moreover, the reference area is configured to calibrate the detection unit, and the reference area is opaque and reflects light falling on the reference area, a detection unit (2, 22) for detecting radiation received from the first marker region and from the second marker region of the marker, as well as block (6) analysis to determine information about the physiological indicators of the subject of the detected radiation from the first marker region and from the second marker region. 2. The system of claim 1, further comprising an image processing unit (4) for recognizing the first marker region (11, 11 ', 23, 34b, 41, 54b, 61b, 71b) and the second marker region (12, 12', 24 , 35b, 42, 55b, 62b, 72b) in the detected radiation. 3. The system of claim 1, wherein the carrier (31, 51) further comprises an adhesive (52) for attaching the carrier to the skin (104) of the subject (100). 4. The system of claim 1, wherein the marker (40) contains the first dye applied on the skin of the subject in the first marker region (41), and the second dye applied to the skin of the subject in the second marker region (42). 5. The system of claim 1, wherein the marker further comprises a graphic pattern (32, 33). 6. The system of claim 1, wherein the first marker region (61b, 71b) and the second marker region (62b, 72b) contain subregions. 7. The system of claim 1, wherein the marker further comprises a stimulator (52) to increase the blood perfusion in the tissue (104) of the subject (100) in contact with the marker (50). 8. The marker (10, 10 ', 30, 40, 50, 60, 70) for determining information (7) about the physiological indicators of the subject (100) configured for use in the system (1) of claim 1, wherein the marker is adapted for overlay on the skin (104) of the subject (100). 9. A device for determining information (7) on the physiological parameters of the subject (100) configured for use in the system (1) according to claim 1, containing the marker according to claim 8. 10. A method for determining information (7) about the physiological parameters of a subject (100) using the system of claim 1, comprising the steps of detecting radiation received from the first marker region; detection of radiation received from the second marker region; determine information about the physiological parameters of the subject of the detected radiation from the first marker region and from the second marker region. 11. A computer-readable medium storing a computer program comprising program code means configured to perform the computer steps of the method of claim 10 when said computer program runs on a computer.

Images